Starts but doesn't run

[nabeel.alsalam]

I'm the new owner of a 1991 50 hp Johnson with electric start. The engine has clearly been well cared for although it was last run a year and a half ago. Apparently, the VRO isn't used (no external oil tank and the oil input has been sort of covered). So I mix the gas 50:1. <br /><br />The motor starts right up but then dies within a few seconds. The fast idle lever doesn't help. It simply bogs down and stalls. Actually, I can keep it running at an unacceptably high rpm if I constantly play with the lever, but it is in danger of overreving. Also, I CAN keep it idling beautifully with the lever all the way down by carefully listening to the rpm and hitting the primer when the rpm starts to drop. <br /><br />I took the carbs apart and they are very very clean. No varnish or crude of any variety. <br /><br />I tested the VRO pump and it squirts lots of gas. The myriad of hoses from the VRO pump seem to be in good shape and securely fastened with the exception of one that goes from the crankcase and I believe is supposed to be connected to the drain hole on the airbox. It is too short and was not attached.<br /><br />Do these symptons suggest where I should be looking next? <br /><br />Thanks for your help.<br /><br />Nabeel

 

[Sherman]

Re: Starts but doesn't run

sounds like air is getting into the fuel line check all the hoses and primer bulb.

 

[Joe Reeves]

Re: Starts but doesn't run

Nabeel..... I would strongly suspect that you are overlooking something within the carburetors. The fact that the engine will stay running whern you energize the primer solenoid (pushing the key in) indicates just that.<br /><br />In the bottom center portion of the float chamber is the fixed brass high speed jet (1 to a carburetor). This is what usually becomes clogged when the engine sits for a few months, and after sitting for over a year it is certain to be fouled, clogged, etc. Fuel must flow thru that jet before it can flow to any other fuel passageway.

 

[nabeel.alsalam]

Re: Starts but doesn't run

Thanks, guys. I will double check the carb and fuel line connections. The carbs are still of the engine. <br /><br />I did not remove the high speed orifice, but I did blow air through it and by shining a flashlight into the top of the float bowl, I verified a nice sized round passageway. <br /><br />Thanks for keeping me on right track. <br /><br />Nabeel

 

[nabeel.alsalam]

Re: Starts but doesn't run

Since last time, I've disassembed the carbs and cleaned them thoroughly, including double checking the brass tube that picks up gas from the float boat. <br /><br />I reinstall the carbs. The engine starts but doesn't run for more than 5 seconds. <br /><br />I'm baffled, so I call a friend over to help me think through the issues. We check the compression -- 130 in one and 140 in the other. Mechanically, the engine seems fine.<br /><br />The spark plugs are wet -- hard to believe the engine isn't getting fuel. We can see a spark arching across the gap. One is weaker than the other and when we switch the two plugs, the weaker spark goes with the plug. Maybe one is too wet. <br /><br />(Later, I take out the plugs and check the gap on the spark plugs and found that they were .036 instead of the recommended .030. I also noticed that the plugs were NGK BR8HS-10 instead of the recommended Champion QL78C or QL78YC.)<br /><br />We check the pressure from one of the 3 output hoses off of the VRO pump -- 4 psi. (We didn't have a T-adaptor to do the test correctly. And we did it by just cranking the engine with the spark plugs removed.) <br /><br />We then do a visual check of gas being squirted from the same output hose. Lots of flow of gas, but there were tiny air bubbles in the gas. We don't know where those bubbles are coming from or whether it is an issue in a system with carbs and float bowls. <br /><br />(Later, I read that the pulse limiter should be checked and cleaned occassionally, but I haven't done that.)<br /><br />We notice that the rubber plug over the external oil supply inlet is cracked. We wonder if that is a source for air in the case. We look for suction from that inlet. There is none. We don't know whether this is an issue related to our problem.<br /><br />The engine starts but doesn't run for more than 5 seconds.<br /><br />Now we notice that gas is dripping from the electric primer. So I need to attend to that.<br /><br />Am I grasping at straws or can the difference in spark plug brand and gap be the cause of the problem? Are the tiny bubbles in the gas from the VRO pump an issue?<br /><br />Thanks for any thoughts or suggestions you can give us.

 

[Walker]

Re: Starts but doesn't run

I suggest you correct all the small problems you have found. Sometimes a bunch of little problems add up to one big problem. If that doesn't solve your problem then I suggest you put kits in the carbs if you already haven't. The gasket on the fuel tower in the carbs must make a good seal betweent the top of the tower and the top section of the carb. Floats must be adjust correctly, and all air leaks must be sealed. Your VRO pump may also have a small crack in the diaphram. Make sure your primer solenoid is working properly. If it is stuck in the open position or the lever is turned the wrong way then fuel will continue to flow thru the primer hose into the intake and it won't run like that.

 

[fireman57]

Re: Starts but doesn't run

You said that the "weaker spark follows". To me this would indicate a weak powerpack. Make sure that the spark is bright blue and jumps a good 7/16 of an inch. If not I would replace the offending powerpack to begin with.